One merely exemplary method that may be used in the manufacture of large, High Volume/Low Speed (HVLS) fans is to attach long airfoil fan blades made by extrusion (or other techniques) to a central hub of cast metal (or other construction). An extruded airfoil, such as one of constant cross section by way of example only, may be cut off at both the inner and outer end, perpendicularly to the axis of the extrusion, or in any other suitable fashion. The outer tip of an airfoil may be finished by the addition of an aerodynamic tip or winglet. Other suitable structures that may be associated with an outer tip of an airfoil or fan blade will be apparent to those of ordinary skill in the art. Of course, the outer tip of an airfoil or fan blade may be simply closed, or may lack any similar structure at all.
In some settings, at the inboard end of a fan blade or airfoil, there may be either a gap between a straight-cut end of the airfoil and a cylindrical outer face of the hub, or else the hub itself may be cast in a polygonal shape in order to meet up with the end of the airfoil. Under some circumstances, these conditions might not be ideal when the assembly of hub and airfoils is in rotary motion; as turbulent airflow, inefficiency, and/or unwanted noise may result under some conditions. Alternatively, the inner end of the airfoil may be cut off in a curve or other configuration matching the outer configuration of the hub surface, but this may impractical in volume manufacture using some techniques.
While a variety of structures and configurations have been provided at or near a junction between a fan blade and a fan hub, it is believed that no one prior to the inventors has made or used the invention recited in the appended claims.
Reference will now be made in detail to various embodiments of the invention, examples of which are illustrated in the accompanying drawings. To the extent that specific dimensions are shown in the accompanying drawings, such dimensions should be regarded as merely illustrative and not limiting in any way. Accordingly, it will be appreciated that such dimensions may be varied in any suitable way.